Thousands of flights were delayed or canceled after a primary line failed and a backup fiber-optic cable was severed

Airport operations across the US north-east resumed Monday evening after a communications line failure snarled flights at some of the country’s busiest airports, leading to thousands of flight cancellations and delays.

Flights were halted at several airports after a primary communications line failed at a key Federal Aviation Administration (FAA) facility in Philadelphia. The backup fiber optic line, which delivers internet service, was inadvertently severed by a railroad construction crew, resulting in a telecommunications crash and hundreds of canceled flights at Newark, LaGuardia, JFK, Philadelphia and Boston airports.